An experimental and modeling study on warping in additively manufactured overhang structures

Printing overhang structures by laser-powder bed fusion (L-PBF) additive manufacturing remains challenging due to warping distortion. This paper studies the warping formation of an overhang structure through in-situ experimental measurements and thermomechanical finite element modeling. For the former, a laser profilometer was utilized for layer-by-layer mapping of the top surface profile of overhang during printing. For the latter, a computationally efficient approach simulating a scaled-down geometry printed with actual laser parameters and scanning patterns was utilized for part-scale moving heat source calculation. The predicted results were validated against the experimental data for various heat inputs. Through analyzing the calculated results of temperature and stress evolutions, it is found that the overhang warping distortion is rooted in bending caused by the non-uniform shrinkage force through the thickness direction and the low structural rigidity of overhang. Additionally, a scanning pause-based method was evaluated, and it is able to suppress the warping at the overhang tip by 30% when employing a scanning pause duration of 5 ms. However, further increasing the scanning pause duration, while decreasing the overhang overheating, does not result in additional reduction in warping distortion.